Method of making magnetic record transducing heads



Feb. 16, 1965 H. w. KOREN ETAL 3,169,303

METHOD OF MAKING MAGNETIC RECORD TRANSDUCING HEADS 2 Sheets-Sheet 1 Original Filed Nov. 21, 1957 FIG.3

INVENTOR. Mid/Worm, BY .ZJM/fIf/HAK ATTORNEYS United States Patent 3,16%,303 METIIGD OF MAKING MAGNETIC RECURI) TRANSDUCENG HEADS Heirnan W. Koren, Huntington, and Ignatius Michalho, Ossining, N.Y., assignors to Sonotone Corporation, Elmsford, N.Y., a corporation of New York Original application Nov. 21, 1957, Ser. No. 697,912. Divided and this application Apr. 26, Edit, Ser. No. 105,647

2 Claims. in. 29 1ss.s

This invention relates to magnetic record transducing heads of the type used for recording magnetic signals or reproducing magnetically recorded signals by magnetic flux interlinkage between the transducing windings of the magnetic head and a relatively wide record track of a magnetic recording medium such as a tape or sheet through relative movement between the head and the recording medium. However, the principles of the invention are also applicable to magnetic erasing heads for erasing magnetic signals previously recorded on a magnetic record track.

This is a division of application Serial No. 697,912 filed November 21, 1957 which application is abandoned.

The heretofore widely used high-quality magnetic tape recording heads have two core sections of a magnetic core held fixed by a resin junction body in a magnetic shield casing of a rigid aligning structure which holds the core aligned in its operative position wherein a portion of the moving magnetic tape makes contact with the transducing gap region of the core which is embedded within the resin body that has an extended smooth guide surface along which the tape is smoothly guided past the transducing gap region of the core exposed along such guide surface. Such known heads have a number of limitations and dcficiencies. Their core sections are upset when the head is exposed to relatively high operating temperatures; they undergo substantial wear during prolonged, continuous operation because of the abrading action of the ferrous oxide particles of the record track of generally used tapes; they also have a volume larger than desirable, particularly in the case of compact magnetic transducers requiring heads of minimized size.

Among the objects of the invention is a high-quality magnetic tape recording head which overcomes the deficiencies and limitations of known heads. Among the objects of the invention is also a tape recording head of the foregoing type, the over-all size or volume of which is only a fraction of the volume of heretofore available heads having similar performance characteristics.

Among the objects of the invention is a head of the foregoing type having simple, fixed electric terminals exposed at the aligning and mounting member of the head and eliminating the cumbersome flexible terminal cables of heretofore available tape-recording heads of this type.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

FIGURE 1 is a greatly enlarged elevational side view of a representative head of the invention, with parts broken away, as it is mounted in its operative aligned position on a bracket of a magnetic recording and reproducing device;

FIGURE 2 is a top elevational view of the head of FIG. 1 with a magnetic tape moving over its guide surface in contact with the transducing gap region of its magnetic core;

FIGURE 3 is an elevational view similar to FIG. 1, of the two poles or the two core sections of the same head held assembled into a self-supporting unit by an aligning junction structure, before positioning it in its aligned posi tion in the aligning casing structure of the head;

3,lh,33 Patented Feb. 16, 1%65 FIGURE 4 is a side view of a core section of FIGS. 1 and 3, along line 44 of FIG. 3;

FIGURE 5 is a view similar to FIG. 1 of the same head before its aligning casing is filled with the resin junction body and before its transducing gap region and its guide surface are given the desired final shape or contour of FIGS. 1 and 2;

FIGURE 6 is a top view similar to FIG. 2 of the head assembly shown in FIG. 5; and

FIGURE 7 is a side View of the head assembly of FIG. 5, with the aligning casing in cross-section and broken away to expose interior details.

FIGURE 3-A is a plan view of the metallic grounding strip that may be used for heads of the invention.

As used herein in the specification and claims, the expressions transdncing head and/or recording head, have the same meaning, and they are intended to mean not only a magnetic recording head suitable for recording magnetic signals or for reproducing them, but also a magnetic head which is used for erasing magnetically recorded signals.

The heretofore generally used high-quality magnetic tape recording heads have a pair of confronting core or pole sections held embedded in a solid resin junction body of a substantially rigid metallic aligning and casing structure with which the head is held mounted in aligned operative position so that the moving tape is smoothly guided over an exposed guide surface of the head past the transducing gap of the core. The metallic aligning structure usually has a magnetic shield casing filled with the cast resin body in which the magnetic core is embedded, the casing having an elongated metallic mounting member, usually in the form of a threaded cylindrical shank arranged to permit ready mounting of the head in its aligned operative position relatively to the moving tape. In the known type of tape recording head, a loop-shaped, nonmagnetic junction sheet member holds the core sections assembled to each other, and the core loop assembly is held by this sheet member within the casing while casting into it the resin which upon solidification holds the core in fixed aligned position relatively to the casing.

According to a phase of the invention, the core or pole sections of a head of the foregoing type are held assembled in their operative position in the aligning casing structure when casting into it and solidifying therein the resin binder, by a simple, elongated aligning member of spring sheet material having a set of two spaced aligning arm portions grippingly engaging and clamping to each other the two core sections of the head, and a set of two other aligning portions which are in aligning engagement with aligning elements of the casing or in general of the aligning structure by which the core sections are held in their aligned position relatively to the moving tape.

In such tape recording heads, the solidified resin body filling its casing is relied upon for fixing the aligned operative position of the transducing gap of its magnetic core sections relatively to its rigid metallic mounting member. Known epoxy resins which are hardened by curing at a temperature in excess of C., such as C.-200 C., are particularly desirable as junction bodies for such magnetic head, because the guide surface of such cured and cast resin has a relatively great hardness desired for guiding the tape along the transducing gap of the magnetic core held embedded in the cast resin. Such epoxy resins have a relatively high thermal coefficient of expansion, two or more times greater than that of the material of the magnetic core assembly. After curing, the cast epoxy resin body at such high temperature in excess of 180 C., the subsequent cooling to normal temperature, such as 20 C. to 30 C., causes the contracting cooled resin body to exert enormous contracting forces on the magnetic core assembly which contracts at a lower rate, resulting in un U controllable variations and disturbance or upsetting of its critical transducing gap region, giving excessive production shrinkage. r V I The magnetic recording medium of most generally used magnetic record types, consists of a layer of fine particles of ferrosoferric oxide Fe O and gamma ferric oxide Fe O which are bonded by a resin binder content to the surface of a supporting tape. The magnetic ferrous oxide particles of such record tape have approximately the same hardness and abrasive action as the crocus particles or alpha ferric oxide which are used as abrasive powder for glass polishing, and is alsoused in What is known as crocus cloth'for polishing metal.

According to the invention, the difliculties to which prior heads of the foregoing type have been subjected as a result of excessive, Wear by the abrasive action of the ferrous particles of the record tape and as a result of thermal differential expansion forces between the resin body and the core operatively' fixed thereby, are minimized and rendered negligible by embodying in the resin junction body filling the head casing, with a dispersion of a critical amount of 50% to 65% and up to 90% of expansion-equalizing and wear-minimizing hard particles such as silica particles having a particle size such as l mesh to 250 mesh, or even finer, such as -35O mesh to 450 mesh particlesize. In practice, very good results are obtained by dispersing in the liquid resin material beforeit is cast into the head casing, 55% to 65% by weight of such silica filler particles. Instead of silica particles, particles of other substances having a similar low coefficient of thermal expansion and similar hardness, may be used, such as aluminium oxide, beryllium oxide, zirconium oxide, zirconium silicate, aluminium silicate, ground quartz, sillim-anite, or mixture of such powder particles.

' Thus, as explained above, by embodying the cast resin junction body dispersion of 50% to 65 by weight of small inorganic filler particles such as si1ica-or the other hard refractory inorganic particles having similar properties with respect to low coelhcient of thermal expansion and resistance to abrasionthere are obtained the combined desirable effects of suppressing the upsetting of the critically minute transducing gap of the core assembly due to differential thermal expansion forces be-.

. tween the core and the cast resin body, and also of suppressing wear of the tape guide surface of the head along which the record tape is guided past the transducing gap region of the core, by the abrading action of the ferrous oxide particles of the magnetic record surface layer of the record tape, or of analogous magnetic recording media.

FIGS. 1 and 2 show a representative magnetic head 25 of the invention mounted in its operative aligned position on a rigid bracket 26 of a magnetic tape recording device having a magnetic recording tape 27 indicated by a dash-doubl-e-dot line,v which moves past a transducing gap 28 of the head in a transducing direction indicated by arrow 27-1 applied to the tape 27.. Although a magnetic head designed for recording on or playing back signals from a magnetic tape, or in general, on a relatively wide magnetic recording medium, will be herein described, the same head structure may also be used for erasing magnetically recorded signals, in which case its magnetic core structure has instead of a minute transducing gap 28, a relatively wide magnetic erasing gap through which its windings are magnetically interlinked with successive magnetic elements of the record track, which are to be erased as they pass the erasing gap of the head.

Referring to FIGS. 1 and 2 and also to FIGS 2-7, showing the same head before a final contour shaping operation-the head 25 comprises two confronting core faces of their pole legs 32 aligned position in its aligning structure 37, which is sections or pole pieces 31 which are shown as two identical halves of a closed magnetic circuit or core loop, generally designated 30. The two core sections or pole pieces 31 are held joined to each other with two end held fixed in the mounting bracket in its properly aligned position relatively to the moving record tape 27. The aligning structure 37 is shown in the form of a casing 38 having casing walls surrounding the core 3t on all sides except along its guide surface 4% on which are exposed the core pole faces 29 with the transducing gap 28 along which the record tape 27 moves. The magnetic core 30 with itswindings is held fixed within the aligning casing 33 by a junction body 3? of nonmagnetic material such as solidified resin, which cements and joins all parts within the casing to each other and to the casing 38.

The aligning casing structure 37 of the head 25 is provided with an elongated aligning member 41 extending from its casing 38 and having a threaded shank 42 held seated in an aligning opening of the supporting bracket 2s, being secured thereto by a nut 43 engaging the threaded shank 42. The part of the mounting member 41 which adjoins the casing 38 has exposed key surfaces corresponding to the exposed key surfaces 434 of the clamping nut 43 so as to make it possible to grip the key surfaces, as with wrench jaws, for turning the head around the shank axis until the transducing gap 28 is brought to the properly aligned position relatively to the moving tape 27, in which position the head 25 is locked by tightening the clamping nut 43.

The magnetic shield casing 38 is secured to the adjoining elongated aligning member 41 in any suitable way. Thus'it may be secured in the manner shown, by providing the inward size of the aligning member 4-1 with a cylindrical metallic extension shaped to fit into a correspondingly shaped circular opening of the casing 33, and to be peened over the edge of the casing opening, in the manner shown in FIGS. 5 and 6, to form a rigid fixed junction between them.

Within'the interior of the mounting member 41 and its shank 42 are held afiixed and mounted, relatively stiff, electrically insulated terminal conductors 4-4, the inner end 44-1 of which are stripped of insulation and have connected thereto, as by soldering, the terminal ends of the coil winding 35. From the exposed outer end of the relatively rigid mounting member, project relatively stiff, stripped metallic terminal pin portions -3-5 of the two terminal conductors 44, and they serve as stiff metallic terminal pins through which the head is connected to associated playback or recording circuits. The inwardly projecting parts of the terminal conductors are offset relatively to their portions which extend through the mounting shank coaxially with their exposed outer terminal pins 45. The two stiff external terminal pins 45 of the head are similar to the exposed projecting terminal pinsof miniature amplifier tubes through which such tubes are connected to the associated amplifier or communication circuits. The playback and recording circuits are:

, readily connected to the terminal pins 45 of the head by a conventional terminal connector socket, such as indicated at 46, which are similar to the conventional miniature connector sockets. Thus, as shown in FIG. 1, the connector socket 46 may consist of a stiff, strong, fiat mounting member of insulating material, such as fibrereinforced synthetic resin, having secured thereto two elastic contact springs 47 of conducting spring sheet metal such as beryllium copper, which have tail portions to which circuit leads are soldered. The two contact springs 4-7 are suitably secured to the insulating socket member 46 as by two hollow rivets =8 shaped to slip with a sliding fit over the two terminal pins 45 while the U-shaped parts of the two contact sprin s 47 are elastically deformed by the terminal pins 45 passing thereover for making positive spring contact engagement therewith.

FIGS. 5-7 show the head of FIGS. 1 and 2, before the open casing side thereof has been ground down to give it the contour of the convex guide face 49 of FIG. 1. As shown in 1 IGS. 5 and 6, and also in FIGS. 3 and 4, the magnetic core loop 3d of the head is originally formed of a material having throughout the length of the core loop the same thickness, and its pole face legs 29 are ground down to the shape shown in FIG. 1 in a later production stage.

Unless otherwise specifically stated, when referring in the following description to the magnetic core loop 39 and to the aligning casing structure 35, it will be assumed that they have the shape shown in FIGS. 2-7, and before they are given the contour shown in FIG. 1. The casing 39 of the aligning casing member 3'7 is made of high-permeability magnetic shield material, and serves as a magnetic shield for suppressing disturbance or interlinkage of disturbing external stray fields with the core 39 and its winding 35. The elongated mounting member $1 with its shank 42 are formed of suitable rigid material so as to secure proper supporting alignment of the head in its support bracket. Good results are obtained by making the mounting member 41 of brass, and the terminal conductors of beryllium copper.

The solid elongated shank 42 of the mounting member 41 is provided with elongated holes 42-1 of larger crosssectional area than the circular, coated terminal conductors 44. After passing the coated insulated terminal con ductors 45 through the oversized perforations 42-1 of the elongated mounting shank 42, the remaining free space of those shank perforations 42-1 is filled with an insulating resin cement which upon solidification joins and fixes the insulated terminal conductors within the shank 42. In practice, the junction body 3% of the head which holds the core 3%? embedded and alignedly fixed therein relatively to the casing and its mounting member ll, is formed by a synthetic resin which is cast in liquid state into the interior of casing 38 while the two core sections 31 are held properly aligned therein until the solidified cast resin forms the fixed aligning junction between them. As the liquid synthetic resin is so cast into the hollow casing 36, the liquid resin fiows also into the free space of the elongated junction holes 42-1 of the aligning shank 42 so that the core structure 30 and the terminal conductors 44 with their terminal pins 45 are held affixed in their operative posit-ion in the aligning structure 36 with its mounting structure 41 by the solidified cast resin body 39.

As seen in FIGS. 1 and Z, the part of the resin junction body 39 filling the interior of the aligning and shield casing 38 which is exposed along the open side of the casing, has a continuous guide surface 48 of utmost smoothness, along which the tape 27 is smoothly guided into and away from smooth contact engagement with the pole faces 2? of the core gap region 28. The two core pole sections 31 are embedded and fixed in the synthetic resin junction body 39 so as to expose the core pole faces 29 as smooth continuities of the smooth guide surface 40 along which the tape is guided toward, past and away from the core gap region 28. After grinding away the exposed side of the head assembly shown in FIGS. 2-6, to give it the contour of the continuous guide surface dd of FIGS. 1 and l-A, this guide surface 48 is subjected to a polishing operation which imparts to this guide surface 413 a polished condition of utmost smoothness which guides the tape with extreme smoothness into intimate contact with the smooth core pole faces 29 of the core gap region 28 as it moves past it.

In accordance with the invention, the sectional core loop 30 has a resilient elongated aligning junction memher 5% or" spring sheet material, such as sheet metal, for holding the two core sections 31 assembled and properly aligned in the open aligning casing 36 until the cast resin is placed and solidified therein. The elongated junction member 50 has a set of two opposing aligning fingers 53 arranged to engage the exterior side surfaces of the two confronting core sections and hold them in their assembled position across their facing leg end surfaces, in the manner shown in FIGS. 3-7. Each of the two core sections 31 of the core loop 3% has an aligning shoulder portion 31-1 arranged so that the two assembled core sections are engaged by the aligning fingers 53 of the spring junction members Ell at these predetermined aligning shoulder portions 31-1 of the two core sections. Furthermore, the resilient elongated aligning junction member 50 is also provided with a set of two opposite aligning portions shaped into aligning engagement with aligning and locating portions 38-1 along the open edge region of the aligning casting 38 of the head aligning structure 41, for fixing the position in which the resilient aligning junction member holds the assembled core section within the casing while the liquefied resin material filling the casing is cast and solidified therein.

In accordance with the invention, the elongated spring junction and aligning member St for the two core sections 31 is arranged so that the major intermediate part thereof is positioned outside and beyond the boundary of the aligning casing 38 of the head 25, for making it possible to reduce to a minimum the over-all volume or size of the head while enabling simplified, mass-production manufacture of miniature size, high-quality magnetic heads with the critical transducing gap 28 in accurate alignment relatively to its aligning structure 41.

In the form shown in FIGS. 3-7, the elongated spring junction member 50 is formed of strong spring sheet metal having good elastic properties, such as beryllium copper. The elongated aligning member 50 is of generally C-shape and it has two inwardly turned arms 51 terminating in two aligning end grips 52 with grip edges 52-1 engaging the flat outer side surfaces of the two core sections 31 for holding them gripped in their assembled position. The aligning member 50 and its two end grips 52 are so arranged that the grips 52 engage the two core sections along the central regions of their outer side surfaces so as to exert balanced gripping forces along a transverse plane extending midway between the two pairs of core end portions 32, 33 of the two core sections 31. This assures that the two core sections 31 are held properly assembled in their aligned operative core-loop position shown, without requiring extreme accuracy in the construction of aligning member 56 and its aligning grip ends 52. In addition, each aligning grip end 52 has two projecting aligning fingers 53 engaging opposite side surfaces 32-2 of the respective upwardly extending pole leg 32 where it adjoins the associated aligning shoulder portions 31-1 of each core section 31. Each grip end portion 52 of spring junction member 50 is shaped so that its intermediate grip end edge 52-1 engages the mid region of the outer surface of the core section 31 gripped thereby; and that its two grip fingers 53 engage with their inward edges the side edge surface 32-2 of the gripped core section, and with the finger end edge 53-1 of the upper aligning surface of the aligning shoulder edge portion 31-]. of the respective core sections. The spring junction member 56 is shown in FIGS. 2-7 in its elastically deformed condition wherein its two end arms 51 are outwardly deformed or bent against their elastic restoring forces so as to embrace with opposite grip ends 52 the mid-part of the outer sides of the two assembled core sections 31 in the region of their aligning shoulders 31-1 along a mid-plane of the two core sections 31 for holding them in the assembled conditions across their facing pole end surfaces, in the manner shown in FIGS. 2-7. When released from this deformed condition, the ends of the junction edge corner at which the respective Wide grip end portions 52 adjoin the narrower end arrns 51 of the aligning member 50. This fixes the aligned position of the spring junction and aligning member 50 and the core assembly held thereby relatively to the aligning casing 38. r 7

Any resin material which may be, prepared to remain for a period of time or pot life, such as one hour or more, in a liquid state in which it will flow and fill all spaces in the interior of the head, such as in the casing 38, and between its various components including the relatively narrow channel spaces through which the insulated terminal conductors 44 pass to the exterior of the head, and which resin material is readily set or cured thereafter isnto ahard, strong junction body holding all adjoining head "elements affixed to each other, may be used for the resin junction body .39 of a head such as described herein. Among resin materials having such properties and suitable for such resin junction body, are epoxy resins which may be cast in liquid state, and polymeiised polyester resins which maybe cast in liquid state, and which will become set into a hard, strong junction body joining all parts with which it makes contact, into a strong, relatively rigid integral solid structure.

Before using such resin for the junction body 39 of'the head, there is dispersed in the liquefied resin material the proper amount of filler particles, such as small silica particles, for minimizing thewear of the guide surface of the head and for minimizing the differential thermal expansion forces developed between the solidifiedphard resin body 39 and the core elements 31 held fixed therein. As stated above, by dispersing in the synthetic resin body, to 65% ofv filler particles of silicaor other hard substances described above, the thermal dififerential expansionforces exerted on the critical core assembly by the hardened resin body in which it is embedded, are minimized to a ne ligible value, and the aligning mounting of the core assembly and its minute transducing gap space 23 is not affected even ifthe head is subjected to large variations in temperature, between room temperature such as 20 C. and a raised temperature such as 8 Resins by Lee and Neville, published 1957 by McGraw- Hill Book Co. 7

Polyester resins having suitable properties are described in the September 1956 Encyclopaedia issue of Modern Plastics, pages 138-143, and in the references given therein, and also in the chart forming part thereof; and also in the September 1955 Encyclopaedia issue of Modern Plastics, pages 176-178, and the chart forming part thereof.

In practice, good results are obtained by using as the resin material for the resin'junction body of the head, the epoxy resins which are commercially supplied in the United States by the Shell Chemical Corporation under the trade-name Epon; by Ciba Company Inc. under the trade-name Araldite; and by Minnesota Mining & Mfg. Company, under the trade-name Scotchcast.

As examples, good results are obtained by using for the resin junction body of the magnetic head of the invention, epoxy resin supplied by Shell Chemical Corporation under the trade-name Epon RN-48, which is liquid at C. and is cured into a hard, strong body by the addition of 5% piperidine, within 24 hours at 80 C., or in 2 or 3 hours at 100 C. Good results are also obtained by using for the resin junction body of the head, epoxy resins supplied by Ciba Company Inc. unded the trade-name Araldite 6019, when mixed with an addition of a curing agent consisting of polyamide 115, or under the trade-name Araldite 502 when combined with an alkaline hardener HN-951, by procedures described in Technical Data Bulletin No. 8 and No. 4, respectively, published by this company. Good results are also obtained by using for the resin junction body of the head, epoxy resins supplied by Minnesota Mining & Mfg. Co. under the trade-name Scotchcast resin CRP 228, consisting of a two-part mixture and which has a pot life from three to four days at room temperature, and i in a liquid state for pouring at 120 C., and is cured into a hard body in from 1 to 2 hours at 120 C.; or Scotchcast resin CRP 232, consisting of a single plastic mixture containing all its hardening ingredients, which is liquid and has a pot life of 2 to 4 hours at 65 C., and

150 C. to 200 C. By embodying in the resin body material such filler particles of a-hard substance such as silica or the other substances referred to above, the exposed guide surface 40 of the head, along which the record tape 27 moves in contact engagement with and past the pole faces of the core gap region 2%, is given such high abrasion resistance as to assure the smooth. guidance of the tape and its perfect contact engagement between the moving tape elements and the pole faces '29 of the core gap region 28 are not disturbed by worn-out surface portions of the tape guide surface 40 during a long useful operating life of the head, such as at least 1000 hours.

Epoxy resins having suitable properties for use as such head junction bodies 39, are described in the September 1956, Encyclopaedia issue of Modern Plastics, pages 105-109, and in the Plastics Properties Chart ofthis issue, under the heading .spoxy Cast Resins; and also in the September, 1955, "Encyclopae'dia issue of Modern Plastics, pages 101-109, and the chart thereof; also in the article by John Charlton, Alloying With Epoxies,

published September, 1954 in Modern Plastics, pages 151-161, 240-243; and in the patents listed on pages 242 and 243 of that article; also in the article Epoxy Resins From Bib, Tris, and Tetrakis-Giycidyl Ethers, by Dearborn et al.,-published December, 1953, in industrial and Engineering Chemistry, pages 2715-2721, and in Epoxy is cured into a hard body within 5 to 8 hours at C.;

'also Scotchcast resin CRP 236, consisting of a single plastic mixture containing all its hardening ingredients, which is liquid and has a pot life of 60 to 70 hours at 65 C. and is cured within a few minutes at a temperature between C..to 200 G, into a hard, strong body.

There will now be described one practical way suitable. for the mass production of high-quality magnetic heads of the type shown in FIGS. 1 and 2, out of the head elements described above in connection with FIGS. 3-7.

In order to uppress undesired noise signals in magnetic record transducing heads of the type shown, the

metallic shield casing 38 is connected to the ground or the grounded side of the amplifier circuit of the associated playback or recording apparatus. Suppression of undesired noise signals also requires a grounding connection between the shield casing 38 and the metallic core leg sections 31 of the magnetic core 30.

In practice, a very effective electric grounding connection between the magnetic core 30 and the grounded shield casing 3% is obtained by applying a metallic conducting paint to the junction regions between the metallic end portions 52 of the aligning spring member 50 which .extend between the core legs 32 and the shield casing38. Suitable conductive paints for this purpose are metallic conductive paints such'as silver conductive paint available on the market. The coating of such metallic conducting paint is applied before filling the interior of the shield casing 38 with the resin junction body 39 which upon solidification joins all parts of the head into a rigid integral structure, Suitable conductive silver paints are, for instancepthose described in US. Patent 2,461,878,

but prepared without the addition of the low melting glass powder. In other words, the paint is formed of the metallizing powder, such a silver powder, held dispersed in a liquid paint medium consisting, for instance, of an organic resin held dissolved in a suitable organic solvent which vaporizes readily and leaves along the coated surfaces a layer of silver powder containing about to of the binder resin. Commercially available conductive metallic paints such as sold by Du Pont de Nemours Company, may be used for this purpose.

As shown in FIGS. 1 and 5, to provide the electric grounding connection, a layer of conductive paint 37-5 is applied at the junction region between the metallic aligning grip end portions 52 of the aligning spring member 50 and the adjacent surfaces of the core legs 42 engaged thereby. The grounding connection is completed by similar layers of conductive paint 38-5 applied to the junction regions between the metallic migning grip end portions 52 and the metallic surfaces of the shield casing 38 engaged thereby. After filling the shield casing with the resin junction body 39 and solidifying it therein, the metallic paint junction elements 37-5 and 38-5 are held embedded in the solidified resin junction body, thus assuring a good metallic grounding connection between the core and the metallic shield casing 38.

Similar conductive metallic paint coatings 44-5 may be applied to the stripped inner metallic ends 44-1 of the terminal conductors 44, for affixing thereto the terminal ends of the transducing coil 35, to assure a good metallic connection between them without a soldering operation. This is an advantage, because the soldering operation frequently results in injury to the fine metallic ends of the conducting wire of the coil 35, which are wound around and have to be metallically joined to the metallic ends 44-1 of the terminal conductors 44.

FIGS. 1, 3 and 3-A show also another Way of providing a metallic grounding connection between the magnetic core 30 of the head and the metallic shield casing 38. It consists of a strip 36-2 of spring metal, such as brass, which has the same width as the inner core Width 33, and is held biased in metallic. contact engagement therewith in the guide channel of the coil bobbin 36. The grounding strip 36-2 is sufficiently long so that when the core assembly of FIG. 3 is placed within the shield casing 38 (FIGS. 1 and 5), the two ends of the grounding strip 36-2 make metallic contact engagement with the side Walls of the shield casing 38. The metallic grounding strip 36-2 has two cut-out tongue portions 36-3 bent outwardly therefrom for preventing substantial longitudinal displacement of the grounding strip 36-2 from its position within the core channel of the coil bobbin 36.

When produced, the two alike and interchangeable complementary core sections 31 are each polished along their two core leg end surfaces so that when assembled into a core loop 34 their end surfaces will make perfect surface contact. The two core sections 31 are then assembled with their inner legs inserted through the oppo side ends of the hollow core of the coil bobbin and the end faces of their two pairs of core legs come in contact engagement along their outer leg end surfaces at the transducing gap 28 and their inner leg end surfaces 33-1, in the manner shown in FIGS, 1-7. A spacing shim of minute thickness may 'be placed between the end faces of the outer core legs 32 at the transducing gap 23 so as to fix its predetermined minute dimension. Af e so assembling the two core sections with the coil 35 seated onthe assembled inner core legs 33, the elongated spring junction member is deformed and positioned with its outwardly bent grip ends 52 against the aligning surfaces at the opposite aligning shoulders 31-1 along the midpart of the two core sections 31 for holding them gripped in their aligned assembled position with the spring junction member Ell in definite alignment relatively to the lb aligning surfaces of the two core sections fill and the transducing gap 28 of the core loop 3b.

In its original condition, shown in FY33. 3-7, as. described above, before shaping its contour the casing 38 of the aligning structure has an edge 538-2 extending beyond the level of the casing edge shown in FIG. 1. As shown in FIGS. 3-7, the original casing edge 33-2 of the original open side of the casing is provided with the set of two opposite aligning cut-outs or slots 33-3 in the opposite parallel side walls of the casing 38 which extend parallel to the adjacent side surfaces of the two core sections 31 and their outer pole legs 32. The casing aligning cut-outs 38-3 have the same width as the transverse width of the outer pole legs 32 and as the main length of spring junction aligning member 58 and its two end arms 51, so that these end arms 51 shall tit into the aligning slots 38-3 when the assembly of the two core sections 31 with their aligning spring junction member B ll is placed in the aligning slots 38-3 within the casing 313. In this aligned casing position, the rear edge surface 52-4 of each finger grip portion 52 of springjunction aligning member 569 has an inclined edge surface 52-4 engaging the inward side of the casing cut-out 38-3 of the open casing edge so that the corner between this inclined edge surface 52-4 and the parallel edge surface of the straight end arm portions 51 of the junction member aligningly engages the opposite side edges of the respective aligning casing cut-outs 38-3. This aligning engagement simplifies and assures proper and aligned positioning of the assembled core sections 31 when they are positioned with their spring junction member 5% in the aligning cut-outs 33-3 of the aligning casing 38, thereby fixing the aligned position of the transducing gap 28 of the core assembly 3t) relatively to the aligning mounting member ll of the head.

Before positioning the core loop and coil assembly with its aligning junction member 5%, such as shown in FIG. 3, in the aligned position within the casing 33, as shown in FIGS. 5-7, there are first inserted into the over-sized passages 4-2-1 of the head aligning shank 42 the outer ends of the two insulated terminal conductors 44 so that their stripped exposed terminal pins 45 project outwardly from the lower end of the mounting shank 42, as seen in FlGS. l and 5, with their inward olfset stripped ends 44-1 projecting upwardly in the casing to about the upper level of the coil bobbin as, as shown in FIGS. 1, 2 and 5-7. Thereupon the core loop and coil assembly with its aligning junction member 55), as seen in FIG. 3, is placed into the interior of the aligning casing 38, as seen in FIGS. 5-7, with the two opposite aligning end portions of the junction member Stl seated in their aligning position within the opposite align ing slots 38-3 of the open casing edge so that the core fill with its transducing gap region 28 are thereby held in the properly aligned position relatively to the alignmg casing structure 38 and its aligning shank 42. After so positioning the core-coil assembly with junction memher 5% in the casing 38, as seen in FIGS. 5-7, the exposed terminal lead ends of the winding coil 35 are metallically joined, as by soldering, to the exposed interior metallic terminal ends 44-1 of the two terminal conductors 44. Thereupon, the interior of the casing 33 is filled with the liquid resin junction body 39 containing the required amount of inorganic filler particles, as de scribed above.

Before filling the casing 38, as seen in FIGS. 5-7, with the liquid resin body, the outer open ends of the channels 42-1 of the aligning shank 42 are sealed, as by applying a readily removable cementitious material, such as pitch, to the exposed end surface of the shank 42 at the region where the exposed terminal pins 45 project therefrom. The aligning slot portions 38-3 along the edge of casing 38 are likewise blocked, as by placing therein gate portions of any suitable sheet material such as impregnated cardboard, metal, or the like, to prevent of the transducer head 25.

11 escape of liquid resin therethrough Afterfilling the interior of the casing with the resin containing the dispersed filler particles, the resin-filled casing and head assembly is subjected to vacuum, as in an evacuated space, to cause gases entrapped by the liquid resin within the casin 38 to escape therefrom so that all spaces within the casing and its terminal conductor channels 424 and all the crevices between the diiferent portions of the core and coil assembly, are filled with the resin body up to the top of the open casing. Thereupon the resin-filled casing and aligning structure 33 with the head assembly I V 369, 36 held inaligned position therein bythe aligning spring junction member 59, are subjected tocuring for the required length of time until the cast resin is fully hardened. This curing treatment is carried on in accordance with the processing instructions provided by the suppliers of the respective epoxy resin compositions, as explained above.

The fully hardened resin junction body joins the core and coil and other elements of the head assembly in their properly aligned position relatively to the'aligning casing 3%and its aligning mounting member 41, 42, in which they are shown in FIGS. -7. Thereupontthe upper part of therassembly, as seen in F168. 5-7, is

' level of the guide solace contourindicated in HS. S'by dasi double-dot tape'path 27, and representing the guide surface ill along which the tape moves past the transducing gap region 2 5 along the adjoining core pole faces 2? exposed along the guide surface of the head, as

seen in FIGS. 1, 2.

The grinding operation also removes a certain amount of the thickness of the outer pole arms 32 along the end portions thereof adjointing the tranducing gap 255 at a level required for optimum high-quality output of thedesired wide frequency range, and providing the exposed core pole faces 29 along which the moving element of the tape make contact with the core loop 349 j as they move past the transducing gap 28. The grindtion over the pole faces 29 of the core loop relativelyto the aligning member ll,

"42, and therethrough to the record tape 27. A simple aligning structure thus makes it possiblezto'retain the "core and coil assembly with the critical transducing gap 2% in properly aligned position relatively to the mounting and aligning member 41, 42 and its aligning cas- "ing when they are assembled in themanner shown, while .the aligning casing is filled with the resin junction body and the latter solidifies. to provide the fixed aligning junction between the critcal elements of the head assembly and the aligning structure 41, 42,.which is turn fixes the aligned position of the transducing gap 28 relatively to the path of the magnetic record, tape 27 while either playing back or making :magnetic'records thereon.

Without thereby limiting the scope of the invention and only in order to enable ready practice thereof, there are given below. specific data of a practical magnetic recording and playback head of the invention of the tape described above in connection with FIGS. 1-7, and designed for recording on or playing back magnetic records from two magnetic record tracks extending side by side on a conventional magnetic tape A" wide, first while one track along one half of the tape moves along the tape path Z'Tpast the pole faces 20 and the transducing gap 28 of the core loop along the guide surface 4!) of the head, and'also while the other track on the other half of the tape Width'similarly moves in the same direcandthe transducing gap 23 of the core loop 3%. t

The transverse over-all dimension of the head in; the direction of the tapepath '27, is .389", and it is .488

' in the direction transverse thereto. The total height 0? the head in'its: axial direction including itsmounting shank, is .725", and the external terminal pins extending from theshank are .2 00" long. The total height of the elongated mounting member 43 with its shank 42 is 11/ The magnetic core loop 36 is jforrned of rolled magnetic sheet material of high'permeability and low T61" tentivity, and consisting of 479 Permalloy, containing as' principal ingredients about 4% molybdenum, about "79% nickel, the balance iron, and minute other additions.- The rolledstock out of which the core loop 3t is made, is about .118 thick. The transverse width of ing operation is followed by a polishing operation The grinding and polishing operation may be sealing cement or pitch from the end face of the aligning shanlcdfi, as by dissolving it with a suitable solvent.

In the head of the invention described above in 'connection with FlGS. 1-7, the still aligning junction memher as fixes the aligned position of the magnetic core loop 349 with its critcal non m'agnetic transducing gap 28 relatively to the head aligning mounting structure '31 and therethrough relatively to the moving magnetic 7 record tape 27. The. aligning junction 'member has a set of two opposite aligning finger elements 52 which are arranged to establish aligning engagement with the core and coil assembly along the two aligning shoulders 31-1 of the core loop assembly 30. The aligning junction member 5% has also av set of two opposite aligning elements formed by outwardly tapering rear edges 52-4 of its aligning finger elements, which enter into aligning engagement with the side edges 38-3 and the bottom edges 3il of the aligning slots 3&1 of the aligning casing 38, thereby fixing the lateral aligned position of the transducing gap 28 of the core loop relatively to the mounting and aligning member 41, head, as well as the aligning level of the pole faces 29 the wider inner'core legs 33 is .120", and the transverse width of the outer core legsf33 is'.090. The. length of the inner core leg. which defines the distance between the plane of the pole 'en'd surfaces of the core legs from the outer side of each core section is :l42".' Themetallic conductor of the terminal pins 45 andof the insulated terminal conductors 44, is of beryllium copper, and has a circular cross-section about .020" in diameter. The insulating'coating consists of a coating layer of nylon extruded thereover, and. the thickness of the coated insulated conductors 44 is about .040", The channel spaces 42-1 of the mounting shank through which the insulated terminal conductor v4,4 passes, are of circular cross-section, and about .080" in diameter. The aligning junction spring 5b is'formed of beryllium copper sheet'stock' .018" thick, and its width in a direction transverse to its length is .090, being equal to the Esimilar transverse width of core pole faces 29; The aligning and gripping assembled'alignment by the aligning junction spring 50.

fingers 53 at each end of the aligning and junction spring 50 have a sliding fit over the upper core legs 32 engaged thereby at the region of their aligning shoulders 31-1 when the two core sections 3 1' are held in clamped and An important feature ofthe'sirnple aligning member which aligns the magnetic'core loop and its critical transducing gap both in the laterally aligned and also in the vertically aligned position relatively .to its aligning member 41, 42, is the'fact thatit also centers v the critical transducing gap of the coreloop relatively to the aligns ing member and thereby. simplifies grinding of the head to the desired contour and the optimum height of the pole '53 and faces along the non-magnetic gap 23 in a direction perpendicular to the path of the tape.

A simple aligning member of the type described above in connection with the two core sections of a core loop of a record transdncing head for transducing records of a single magnetic record track, may be modified in accordance with the invention so that each of its gripping fingers 52 has a grip edge 52-1 wide enough to grip two nearby core sections 31 of two independent core loops, of two adjacent transducing core units, each interlinked with its own windings for recording two complementary stereophonic magnetic signal records on two adjacent stereophonic record tracks, and/or for playing back two stereophonic signal programmes from such two stereophonoic record tracks.

We claim:

1. In the production of a magnetic record transducing head comprising a casing with an open casing face and holding in its casing interior a magnetic core loop having two confronting core sections with one set of confronting pole faces separated by a transducing core gap extending transversely to a fiat surface of a magnetic record medium moving past one edge of said core gap exposed along said casing face and an opposite set of confronting pole faces at the opposite ends of said two core sections held in the deeper casing interior,

the procedure comprising assembling the two core sections and their windings into the core loop which is interlinked with said windings,

clamping the two so-assembled core sections across their two sets of substantially plane confronting pole faces by an elongated clamping spring having an intermediate spring region overlying the exposed edge of said transducing gap and having two opposite spring grip ends embracing middle portions of the two assembled core sections and thereby exerting on 14 said two sets of confronting pole faces pressure forces solely in a direction perpendicular to each of said two respective sets of pole faces, inserting the so clamped assembled core'loop into the casing interior and bringing the opposite end regions of said spring into aligning engagement with aligning sidewall portions of said casing to fix said core loop in a predetermined aligned position relative to said casing, while leavingsaid intermediate spring region outside said casing,

filling the interior space of said casing with said assembled core loop and said spring end region held therein with a fluid resin body and solidifying the resin body in said casing to afiix said core loop in said aligned position within said casing,

thereafter removing said intermediate spring region together with excess of solidified resin and excess of adjacent casing sidewalls and forming along the ex posed solidified resin continuous smooth guide surface along which the opposite core portions having said one set of pole faces are exposed to engagement with the moving recording medium.

2. In the production oi. a magnetic record transducing head as claimed in claim 1, the step of embracing the two core sections including engaging with said opposite spring grip ends the midportions of said two core sections spaced approximately midway between their two sets of opposite pole faces.

Kornei Dec. 23, 1958 

1. IN THE PRODUCTION OF A MAGNETIC RECORD TRANSDUOING HEAD COMPRISING A CASING WITH AN OPEN CASING FACE AND HOLDING IN ITS CASING INTERIOR A MAGNETIC CORE LOOP HAVING TWO CONFRONTING CORE SECTIONS WITH ONE SET OF CONFRONTING POLE FACES SEPARATED BY A TRANSDUCING CORE GAP EXTENDING TRANSVERSELY TO A FLAT SURFACE OF A MAGNETIC RECORD MEDIUM MOVING PAST ONE EDGE OF SAID CORE GAP EXPOSED ALONG SAID ASING FACE AN AN OPPOSITE SET OF CONFRONTING POLE FACES AT THE OPPOSITE ENDS OF SAID TWO CORE SECTIONS HELD IN THE DEEPER CASING INTERIOR, THE PROCEDURE COMPRISING ASSEMBLING THE TWO CORE SECTIONS AND THEIR WINDINGS INTO THE CORE LOOP WHICH IS INTERLINKED WITH SAID WINDINGS. 